An impact wrench is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user by storing energy in a rotating mass or hammer that is delivered suddenly to an output shaft or anvil. A socket is attached to the anvil, and the rotating hammer is accelerated by a motor and then suddenly connected to the anvil creating a high torque impact to the anvil and, in turn, to the socket attached to the anvil. The hammer mechanism is designed such that after delivering the impact the hammer is again allowed to spin freely. With this design, the only reaction force applied to the body of the tool is the motor accelerating the hammer, and thus the operator feels very little torque, even though a very high peak torque is delivered to the socket. Compressed air is the most common power source for impact wrenches, although electric and hydraulic power is also used, with cordless electric impact wrenches becoming more popular.
Various attachment systems are used to attach sockets to the anvils of impact wrenches. Common attachment systems include a spring-loaded pin incorporated in the anvil that snaps into a corresponding hole formed in the socket, or a snap ring which holds the socket by friction or by snapping into indents machined into the socket. A typical snap ring is a severed ring formed of rugged spring steel, which must be installed so as to encircle an O-ring located in an annular groove formed in the anvil. Installing a snap ring onto the O-ring located in the annular groove formed in the anvil of an impact wrench is notoriously difficult and time consuming due to the rugged and resilient characteristics of snap rings and limited locations at which to grasp or hold the snap ring. Accordingly, it would be highly desirable to provide a quick, efficient, inexpensive, and easy way to install a snap ring onto the O-ring located in the annular groove of an impact wrench.